The quantitative morphology contributes to making the studies less subjective and reproducible. Quantitative results are analyzed with statistics and should be based on a well-defined sample. Quantitative variables can be ‘continuous’ or ‘discrete.' In this text, the term ‘morphometry’ is used to design a simpler procedure for measuring structures with a ‘ruler.' The term ‘stereology’ is used in estimating quantities in the 3-dimensional space analyzing 2-D cut sections. Correction factors may be necessary for the retraction and compression of the tissues. In histological sections, the ‘caps’ of the objects that have been sectioned tangentially are lost when chemical agents remove the paraffin distorting the analysis. Moreover, the analyses based on digital images should consider the same format and the same size (pixels) to all pictures allowing a comparison between groups. Stereology can be ‘model-based’: points within a frame are counted to estimate the ‘volume density’ (Vv) of a structure, and intercepts are counted to assess the ‘surface density’ (Sv). Counting structures within a frame allow estimating the ‘length density’ (Lv). Newer and more complex ‘design-based’ procedures are considered unbiased. The key point is that design-based inference does not require assumptions about the material and uses the ‘random sampling’ approach. The estimation of the number of objects requires a 3-D (volume) probe and therefore the ‘disector ’ technique. This review aimed to contribute to the execution of the project, the correct sampling and the data obtained with morphometry and stereology.
KEY WORDS: Sample size; Digital images; Statistics; Model-based stereology; Design-based stereology.